We study in this paper the effect of weak, short-ranged interaction on disordered metals. Through analyzing the interaction matrix elements between different eigenstates of the noninteracting and corresponding Hartree-Fock single-particle Hamiltonian, we argue that as a result of localized single-particle eigenstates around the Fermi surface, the quasiparticle states on the Fermi surface are unstable toward formation of magnetic moments for arbitrary weak (but finite) repulsive interaction in the thermodynamic limit. This is a mechanism very different from the case of strong interaction $U\sim W_B$ ($W_B=$ bandwidth) or the quantum Griffiths effect where local moments are formed at small localized regions where coupling to the surrounding is weak. Numerical simulations are performed to verify our analysis. We further propose within a Landau Fermi-liquid-type framework that our result is applicable for general electronic systems with weak, short-ranged interaction as long as the quasiparticle states exist and are localized. An analogous result is obtained for attractive interaction, suggesting that Fermi glass state is intrinsically unstable in arbitrary dimension.

The tetragonal heavy-fermion compound ${\mathrm{CeRh}}_2{\mathrm{As}}_2$ has intriguing low-temperature symmetry-breaking phases whose nature is unclear. The unconventional superconducting phase is complemented by other normal-state phases which presumably involve ordering of $4f$ electron multipoles supported by the Kramers doublets split by the tetragonal crystal electric field (CEF). The most striking aspect is the pronounced anisotropic $H\text{−}T$ phase boundary for in-plane and out-of plane field directions. Using a localized $4f$ CEF model we demonstrate that its essential features can be understood as the result of competing low-field easy-plane magnetic order and field-induced quadrupolar order of $xy$ type. We present calculations based on coupled multipole random phase approximation response function approach as well as molecular field treatment in the ordered regime. We use an analytical approach for a reduced quasiquartet model and numerical calculations for the complete CEF level scheme. We discuss the quantum critical properties as function of multipolar control parameters and explain the origin of a pronounced ac anisotropy of the $H\text{−}T$ phase diagram. Finally, the field and temperature evolution of multipolar order parameters is derived and the high-field phase diagram is predicted.

Rare-earth tritellurides represent quasi-two-dimensional systems that exhibit multiple charge density wave (CDW) transitions alongside magnetic ordering. However, the interplay between the phonon dynamics of collective excitations and local magnetism remains unclear. ${\mathrm{GdTe}}_3$ is an interesting material having an incommensurate CDW (ICDW), at $T_{\mathrm{ICDW}}\sim 380$ K, an antiferromagnetic transition at $T_N\sim 13$ K, and with an expectation of another CDW ordering. We emphasize electron-spin-phonon and mode coupling in ${\mathrm{GdTe}}_3$ through temperature dependent Raman spectroscopy complemented by heat capacity and magnetization measurements. Disappearance of zone-folded mode (Z*) and observed coupling behavior of amplitude mode suggest the existence of another ordering at $\sim 240$ K, in addition to known ICDW. By employing phonon renormalization, we estimated significant strength of spin-phonon coupling, $({\lambda }_{\mathrm{s}-\mathrm{ph}}\sim 0.234)$ and accentuated on the phonon dynamics associated with CDW instabilities in ${\mathrm{GdTe}}_3$.

Rare-earth tetraborides $\left({R\mathrm{B}}_4\right)$ have attracted a lot of recent attention due to their intriguing electronic, magnetic, and topological properties. We have theoretically investigated the topological properties of ${\mathrm{PrB}}_4$, which is unique among the ${R\mathrm{B}}_4$ family due to its ferromagnetic ground state. We have discovered that ${\mathrm{PrB}}_4$ is an intrinsic magnetic Weyl system possessing multiple topological band crossings with various chiral charges. Density-functional-theory band calculations combined with a tight-binding band analysis reveal large Fermi-arc surface states, which are characteristic fingerprints of Weyl fermions. Anomalous Hall conductivity is estimated to be very large, ranging from 500 to $1000{\left(\mathrm{\Omega }\mathrm{cm}\right)}^{-1}$ near the Fermi level, which also demonstrates the topological Weyl character of ferromagnetic ${\mathrm{PrB}}_4$. These findings suggest that ${\mathrm{PrB}}_4$, being a potential candidate of a magnetic Weyl system, would be a promising rare-earth topological system for applications to next-generation spintronic and photonic devices.

Knowledge of the ground state of lanthanides (Ln) in Ln-based materials is fundamental for understanding their properties, particularly those related to magnetism. In crystalline materials, the magnitude and orientation of $4f$ magnetic moments are often strongly influenced by the crystal electric field (CEF), making them challenging to predict ab initio. This complexity is intensified in low-dimensional systems and nanostructures, where the CEF may vary significantly near surfaces and at interfaces. The related variations of the $4f$ ground state should be probed by methods with adjustable surface sensitivity. Here, we apply x-ray absorption spectroscopy (XAS) at the Ln $4d$ edge, along with modeling of XAS spectra, to probe the $4f$ ground state of Ln atoms both at the surface and in the bulk of ${\mathrm{LnRh}}_2{\mathrm{Si}}_2$ layered crystals. Our results explicitly reveal significant changes of the $4f$ ground state, which may lead to the reorientation of $4f$ moments at the surface compared to the bulk, driven by alterations of the CEF. We also provide a comprehensive database of calculated Ln $4d$ XAS spectra in numeric format for all lanthanides. Our findings will facilitate studies of Ln-based materials and molecular complexes by enabling comprehensive analysis of XAS data, including those obtained through magnetic linear and circular dichroism techniques, as well as related spectromicroscopy studies.

By merging algorithmic Matsubara integration with discrete pole representations we present a procedure to generate fully analytic closed form results for impurity problems at fixed perturbation order. To demonstrate the utility of this approach we study the Bethe lattice and evaluate the second-order self-energy for which reliable benchmarks exist. We show that, when evaluating diagrams on the Matsubara axis, the analytic sums of pole representations are extremely precise. We point out the absence of a numerical sign problem in the evaluation, and explore the application of the same procedure for real-frequency evaluation of diagrams. We find that real-frequency results are subject to noise that is controlled at low temperatures and can be mitigated at additional computational expense. We further demonstrate the utility of this approach by evaluating dynamical mean field and bold diagrammatic self-consistency schemes at both second and fourth order and compare to benchmarks where available.

For the three-terminal NSN device with single-mode normal terminals and without Coulomb blockade, we propose the interpretation of charge transfer process, which allows us to consistently characterize the device operation as that of a Cooper pair splitter in terms of scattering matrix elements as well as in terms of measurable quantities. The obtained explicit expression for the splitting probability notably contains the two-particle interference term not available from conductance measurements. We show that splitting does not necessarily rely on single-particle crossed Andreev reflection amplitude thus allowing for the unit efficiency at zero energy. Our results imply that the current cross correlator generally does not provide definite measure of splitting.

A promising route towards the realization of chiral spin liquids is the quantum melting of classically noncoplanar spin states via quantum fluctuations. In the classical realm, such noncoplanar orders can effectively be stabilized by interactions beyond nearest neighbors. Motivated by the recent synthesis of materials with a maple-leaf lattice geometry, we study the effect of cross-plaquette couplings on elementary Heisenberg antiferromagnets for this geometry (as well as their ferromagnetic counterparts). We find a rich spectrum of noncoplanar states, including an icosahedral order as well as incommensurate spin spirals, using large-scale Monte Carlo simulations in combination with a semianalytical analysis. To inspect the potential quantum melting of these states, we analyze the quantum $S=1/2$ variant of these models using pseudofermion functional renormalization group simulations. Notably, we indeed find extended parameter regimes lacking long-range magnetic order—in regions classically occupied by noncoplanar orders—which we putatively identify with the possible formation of chiral quantum spin liquids.

We present a scheme for projective quantum Monte Carlo (QMC) simulation that combines unbiased zero-temperature (projective) determinant QMC with variational Monte Carlo based on the Gutzwiller projected wave function. This approach is dubbed as Gutzwiller-projection QMC. Our numerical results demonstrate that the use of the Gutzwiller projected trial wave function significantly accelerates the convergence of computational results, thereby greatly reducing computational time in the simulation. Moreover, we provide an illustrative example showing that the sign problem is substantially mitigated in the Gutzwiller-projection QMC. We believe that the Gutzwiller-projection QMC opens up another pathway for enhancing efficiency and alleviating the sign problem in QMC simulations of interacting fermionic systems.

We reconsider derivation of Ward identities for spin stiffnesses, which determine the nonlinear sigma model of magnetic degrees of freedom of interacting electrons in the presence of antiferromagnetic or incommensurate correlations. We emphasize that in the approaches, which do not break explicitly spin symmetry of the action, the spatial components of gauge kernel, which are used to obtain spin stiffnesses, remain gauge invariant even in case of spontaneous spin symmetry breaking. We derive the corrected Ward identities, which account for this gauge invariance. We find that the frequency dependence of temporal spin stiffnesses is not fixed by the obtained identities, and show that the infinitesimally small external staggered field is crucially important to obtain finite static uniform transverse susceptibility. On the other hand, the spatial spin stiffnesses are determined by the gauge kernel of the Legendre transformed theory, which is in general different from the gauge kernel of the original theory and obtain an explicit expression for spatial spin stiffnesses through susceptibilities and current correlation functions. We verify numerically the obtained results within dynamic mean-field theory, and obtain doping dependencies of the resulting spin stiffnesses for antiferromagnetic and incommensurate phases.

The polarizability of nearby ions may have a significant impact on electron interactions in solids, but only limited experimental data are available to support this picture. In this work, using a highly simplified description of the prototypical FeAs superconducting layer, we show how external optical excitation of the As $4p\text{−}5s$ splitting can lead to a significant modulation of the polarization-mediated effective interactions between carriers. Our results suggest that even perturbative external fields, approximately 2 orders of magnitude smaller than the internal field generated by charge carriers, might enable the exploration of the role of the anion's polarizability in determining the correlated physics, although more detailed modeling is needed to decide the optimal ways to achieve this.

Effective control of interlayer interactions is a key element in modifying the properties of van der Waals heterostructures and the next step toward their practical applications. Focusing on the phosphorene-${\mathrm{WSe}}_2$ heterostructure, we demonstrate, using first-principles calculations, proximity-induced amplification of the spin-orbit coupling in phosphorene by applying vertical pressure. We simulate external pressure by changing the interlayer distance between bilayer constituents and show that it is possible to tune the spin-orbit field of phosphorene holes in a controllable way. By fitting effective electronic states of the proposed Hamiltonian to the first-principles data, we reveal that the spin-orbit coupling in phosphorene hole bands is enhanced more than two times for experimentally accessible pressures up to 17 kbar. Correspondingly, we find that the pressure-enhanced spin-orbit coupling boosts the Dyakonov-Perel spin relaxation mechanism, reducing the spin lifetime of phosphorene holes by factor 4. We further explore the role of the lateral shift on the spin-orbit field and reveal that the spin-orbit strength of phosphorene holes can be sizably modulated when strong pressure is applied. We also found that the thermopower is governed mainly by the phosphorene and pressure reduces the overall thermoelectric efficiency of the heterostructure.

We investigate the effect of Coulomb drag resistance in a bilayer system of strongly correlated electron liquids magnetized by an in-plane field employing the framework of hydrodynamic theory. We identify a mechanism for drag magnetoresistance, which physically arises from the spin diffusion driven by fluctuations of the spin currents within a partially spin-polarized fluid. This effect is further enhanced by acoustic and optic plasmon resonances within the bilayer, where hydrodynamic plasmons are driven by fluctuating viscous stresses. We express the drag magnetoresistivity in terms of the intrinsic dissipative coefficients and basic thermodynamic properties of the electron fluid. Our results are derived nonperturbatively in interaction strength and do not rely on assuming Fermi-liquid behavior of the electron liquid, and applicable also in the regimes of semiquantum and highly correlated classical fluids.

We theoretically study polaron spin states in chiral systems for both weak and strong electron-phonon coupling using the well-known Lee-Low-Pines unitary transformations, where the strain tensor induced by the phonon displacement of chiral structures couples directly with the electron spin. We find that the splitting magnitudes of polaron spin states are enlarged significantly with increasing the cutoff wave vector of phonon modes, which directly relate to several key ingredients of the polaron transport for chirality-induced spin selectivity (CISS), such as the lifetime of spin filtering and the effective masses of spin states. These results not only provide a potential CISS mechanism based on direct spin-phonon coupling, but also enrich fundamental physics of polaron studies in various chiral systems.

In recent years, non-Hermitian phases in classical and quantum systems have garnered significant attention. In particular, their intriguing band geometry offers a platform for exploring unique topological states and unconventional quantum dynamics. However, their topological characterization becomes particularly interesting and challenging in complex multiband systems. Here we propose a decimation framework, which leverages real-space renormalization group to streamline the analysis of complex multiband non-Hermitian systems. Our systematic approach allows us to probe different phases and transitions, analyze bulk-boundary correspondence, formulate generalized Brillouin zones, investigate open boundary spectra, survey non-Bloch van Hove singularities, study disorder-induced effects, and explore tunable non-Hermitian flat-band physics. Additionally, our framework allows proposing a hypothesis about quasi-one-dimensional bipartite non-Hermitian systems with flat bands, demonstrating their decoupling into Su-Schrieffer-Heeger chains and compact localized states across various models. Our paper presents a powerful and comprehensive framework for understanding the intricate properties of non-Hermitian multiband systems, offering insights into the evolving landscape of non-Hermitian topological physics.

Atomic forces and energies, calculated by interatomic potential, are fundamental components of molecular dynamics (MD) and Monte Carlo (MC) simulations. Compared with traditional potentials, machine-learning (ML) potentials trained by using extensive density-functional theory databases exhibit high accuracy in predicting physical and chemical properties of materials, but their transferability often faces constraints. To address this limitation, physically informed neural network (PINN) potentials have been developed. These models synergistically combine the strengths of ML with physics-based bond-order interatomic potentials, aiming for both improved accuracy and broader applicability. However, a major limitation remains: the low performance of PINN potentials, hindering large-scale simulations. This work introduces a potential framework by incorporating an artificial neural network (ANN) into typical potential functions, which not only improves the transferability compared with the ANN potential, but also significantly improves the performance of ML potentials. The developed ANN assistant potential for body-centered cubic (bcc) iron demonstrates exceptional accuracy in property predictions while boasting remarkable computational efficiency. Its performance utilizing a single graphics processing unit (GPU) card overcomes both 12-message passing interface central processing unit -only ML potential and GPU-accelerated ML potential by achieving speedups of 201× and 26×, respectively. The proposed approach has a potential to provide a powerful way to develop high accurate and efficient potentials even in the other systems.

Stable compounds comprising nitrogen, sulfur, and hydrogen elements hold significant promise in hydride superconductors and astrophysical matter. Herein, we utilize a blend of structure prediction techniques and first-principles calculations to comprehensively explore the N–H–S system. We present the discovery of two ionic compounds, ${\mathrm{NH}}_4\mathrm{S}$ and ${\mathrm{NH}}_4{\mathrm{S}}_2$, characterized by similar ${\mathrm{NH}}_4$ configurations but distinct arrangements of sulfur atoms. As the sulfur content increases, we observe a transition in the bonding pattern of sulfur-sulfur interactions from ${\mathrm{S}}_2$ dimers to ${\mathrm{S}}_4$ units. Furthermore, the electron transfer from ${\mathrm{NH}}_4$ to each S unit escalates from 1.04 $e$ $\left({\mathrm{NH}}_4\mathrm{S}\right)$ to 1.24 $e$ $\left({\mathrm{NH}}_4{\mathrm{S}}_2\right)$. Through ab initio molecular dynamics simulations, we unveil a sequence of phase transitions encompassing solid, superionic, and liquid phases for both compounds. Notably, the high-pressure and high-temperature phase diagrams reveal that only the superionic phase of ${\mathrm{NH}}_4\mathrm{S}$ corresponds to the extreme conditions found in the interior of the Earth. Moreover, the liquid regions of both compounds encompass the isentropic lines of Neptune, Uranus, and Jupiter. These results could provide essential information for understanding the N–H–S system at high pressure and the formation models of the planets.